mwifiex: fix wrong eth_hdr usage for bridged packets in AP mode

commit 8d93f1f309d38b65fce0b9f0de91ba6c96990c07 upstream.

The eth_hdr is never defined in this driver but it gets compiled
without any warning/error because kernel has defined eth_hdr.

Fix it by defining our own p_ethhdr and use it instead of eth_hdr.

Signed-off-by: Ujjal Roy <royujjal@gmail.com>
Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>